Debt (Narrative) (Details)			9 Months Ended
	May 04, 2017 USD ($)	Jan. 19, 2010 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	May 03, 2017 USD ($)	Dec. 31, 2015
Line of Credit Facility [Line Items]
Long-term Debt, Gross			$ 17,679,000		$ 13,705,000
Debt Issuance Costs, Net			(82,000)		(131,000)
Long-term Debt			17,597,000		13,574,000
Proceeds from revolving facility			17,500,000	$ 12,500,000
Amount of line of credit outstanding			17,549,000		13,526,000
Long-term Debt, Current Maturities			48,000		48,000
Long-term Debt, Excluding Current Maturities			17,631,000		13,657,000
Long Term Debt, Excluding Current Maturities Net of Debt Issuance Cost			17,549,000		13,526,000
SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Credit facility, term		4 years
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross			17,600,000		13,600,000
Debt Issuance Costs, Net			(82,000)		(131,000)
Long-term Debt			$ 17,518,000		13,469,000
Line of Credit [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Interest rate during period			4.35%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.25%
Capital Lease Obligations [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross			$ 79,000		105,000
Debt Issuance Costs, Net			0		0
Long-term Debt			79,000		$ 105,000
Sun Trust Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Amount of line of credit outstanding			17,600,000
Line of credit remaining borrowing capacity			$ 17,400,000
Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity of credit facility	$ 35,000,000.0	$ 15,000,000.0				$ 20,000,000.0
Sun Trust Term Loan [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount		$ 15,000,000.0
Long-term debt, weighted average interest rate							0.25%
Minimum [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)			1.75%
Pricing Level One | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Leverage Ratio	1.25
Applicable Percentage For Commitment Fee	0.25%
Pricing Level One | London Interbank Offered Rate (LIBOR) [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	2.25%
Pricing Level One | Base Rate [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	1.25%
Pricing Level Two | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable Percentage For Commitment Fee	0.375%
Pricing Level Two | London Interbank Offered Rate (LIBOR) [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	2.50%
Pricing Level Two | Base Rate [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	1.50%
Pricing Level Two | Minimum [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Leverage Ratio	1.25
Pricing Level Two | Maximum [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Leverage Ratio	1.75
Pricing Level Three | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Leverage Ratio	1.75
Applicable Percentage For Commitment Fee	0.375%
Pricing Level Three | London Interbank Offered Rate (LIBOR) [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	2.75%
Pricing Level Three | Base Rate [Member] | Sun Trust Revolving Credit Facility [Member] | SunTrust Bank [Member]
Line of Credit Facility [Line Items]
Applicable margin (percent)	1.75%